In the field of network storage devices, the SAS protocol is a serial connection protocol utilized to transfer digital data between network storage elements (hereinafter referred to as SAS storage devices). The SAS protocol requires that a link negotiation method be performed before communication is enabled between SAS storage devices. The link negotiation method: establishes the presence of other SAS storage devices; and synchronizes SAS storage devices so that communication is enabled between SAS storage devices within a controlled period of time.
Such a link negotiation method also facilitates the return of a SAS storage device to an initial reset state when communication between SAS storage devices fails. This helps ensure that the SAS storage devices are synchronized (i.e. two SAS storage devices have communication enabled or neither SAS storage device has communication enabled). Initiation of the link negotiation method by one SAS storage device will induce another SAS storage device to also initiate the link negotiation method.
The link negotiation method described in version 2.0 of the SAS protocol is suitable for SAS storage devices that are connected by electrical cables, but is unsuitable for enabling communication between SAS storage devices that are connected by optical cables because it utilizes a direct current (D.C.) idle electrical state that cannot be represented by a light pulse.
The link negotiation method described in version 2.1 of the SAS protocol provides a link negotiation method that is suitable for SAS storage devices that are connected by optical cables. The link negotiation method described in version 2.1 of the SAS protocol replaces every instance of a D.C. idle electrical state of the link negotiation method described in version 2.0 of the SAS protocol with a distinctive data pattern that is not previously defined in version 2.0 of the SAS protocol. The link negotiation method described in version 2.1 of the SAS protocol, however, is incapable of enabling communication with legacy SAS storage devices that utilize the link negotiation method described in version 2.0 of the SAS protocol to enable communication.
Improvements in link negotiation methods for enabling communication between SAS storage devices that are connected by optical cables and utilize the SAS protocol to transfer digital data between SAS storage devices are therefore desirable.